docs(plugins/Data): add documentation

Related to CAM-1558
chore(CONTRIBUTING): change EasyPick link
chore(engine): improve logging for PA-Context-Switch

- Logg PA context switch details on LOGG Level FINE.
improve(engine): add comma to registrations logging
chore(maven): use correct junit dependency
chore(maven): cleanup cdi module pom
chore(maven-central): override plugin invocations from sonatype parent pom

related to CAM-1250
fix(engine/compensate): resolve activityRef in correct scope

handle cases where referenced activity
* is part of parent scope
* is part of a nested scope

closes #CAM-1409
chore(oracle-xa-datasource): adjust configuration as proposed by JBoss

related to CAM-1621
fix(engine-rest): standalone authentication tests use different executions

related to CAM-1557
chore(plugin/resouces): Get plugin resources by using ClassLoader

- get plugin resources as stream by using the ClassLoader of the
  CockpitPlugin SPI implementation
- at first the mechanism try to load the resources from classpath, if the
  result is equal null then it will load the resources from the webapp, so that the prefix "webapp://" is unnecessary.
- adjust test cases

related to CAM-1420
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
chore(engine/callActivity/variables): Cleanup code

related to CAM-1617
chore(jbosseap62): replace jboss method with our own abstraction

- replace Services.addServerExecutorDependency with our own abstraction because the method signature
  from JBoss AS 7.2.0.Final / EAP 6.1 differs from EAP 6.2. The error occurs at runtime only because
  the return value of the method is compiled into the bytecode, so at runtime the method signature is
  not only the name + parameters, but return value too.

related to CAM-1599
fix(engine-rest): comment occasionally failing mock verification

related to CAM-1557
fix(engine): Properly end pruned execution after parallel gateway join

- use the ExecutionEntity end() instead of remove() function to clean pruned
  executions
- the end() function will correctly call the AtomicOperation ACTIVITY_END,
  which will trigger a database update for the endtime
- add test case and process from  https://app.camunda.com/jira/browse/CAM-1537
- set isEnded flag in ExectuinEntity deleteCascade() function to
  prevent an additional deletion attempt

Closes #CAM-1537
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
fix(historic/testcase): move test case to historic activity instance

related to CAM-1537
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
chore(renderer): update to latest version